Phosphorus (P) is commonly found in municipal and agricultural wastewater, originating from the digestion of phosphorus-containing food sources. Soluble reactive phosphorus, typically in the form of orthophosphate (PO4+3), can be a nutrient for aquatic plants, such as algae, which can be either a health risk to aquatic life or an aesthetic nuisance to those living near or using the waterways. In the case of blue-green algae, toxic by-products can be produced, which create health issues if a lake or reservoir would be used as a source of drinking water.
Control of phosphorus can be achieved by forming a precipitant when the soluble phosphorus, in the form of orthophosphate, combines with a soluble metal, such as aluminum or iron. Several coagulants are also applicable to remove phosphorus from wastewater or sewage.
Aluminum sulfate is commonly used for phosphorus control due to its low metal to phosphorus ratio required for formation of a precipitant. It is widely used in some wastewater treatment plants and municipal sewage treatment plants for removing phosphorus. In these plants, aluminum sulfate needs to be added into wastewater, or secondary treated or tertiary treated effluent in certain methods. The chemical needs to be added to a treatment unit constantly. In on-site sewage treatment plants, it is difficult to use special equipment to add any coagulant for phosphorus removal treatment. Therefore, a special composition, form and method need to be developed to carry out the phosphorus removal task in on-site sewage treatment plants.